This invention relates to a pipe coupling for joinder of adjacent end segments of pipe. It pertains particularly to such a coupling which self locks upon assembly to prevent subsequent disassembly of the segments.
In joinder of lengths of pipe end to end to form a long run of pipe, particularly pipe fabricated from plastics such as polyvinylchloride, no completely satisfactory means has been devised to join the end segments of the pipe. Heretofore, the most common method of joining lengths of plastic pipe consists of applying a coating of cement to the peripheral end portion of one of the lengths and inserting that length into an enlarged bell at one end of the other length. The two lengths are then coupled when the cement dries.
Cement has the disadvantage that good workmanship is necessary to form a reliable coupling. On large pipes the time required to apply the cement and assemble the lengths of pipe may result in partial drying of the cement before assembly. Thus the joint is not completely formed. Repair in this event is impossible since the cement that has bonded prevents separation of the two sections.
Another common method of joining pipe lengths is by use of an elastomeric seal, such as an O-ring gasket. The seal is placed in a grooved recess located at the entrance of an enlarged bell section in the end of one of the pipe lengths. The adjoining length is then inserted into the enlarged bell end, compressing the seal so that a leak-proof connection is made.
An O-ring seal is more reliable than a cement joint. However, it will not resist end thrust, so blocking must be provided at a bend or any place where internal pressure results in the application of an axial load across the joint. Therefore, the use of this type of coupling results in additional expense in installation of the pipe.
The use of a pliable seal which relies on a differential in the coefficient of friction between its outer surface and its inner surface to allow wedging of the seal between the lengths of pipe when separation of the joined lengths of pipe is attempted is known in the prior art. In particular, U.S. Pat. No. 3,064,983 teaches this concept.
However, the prior art pipe couplings using a seal of this type have relied on a large difference in the coefficient of friction between the inner and outer surfaces of the seal. This difference often must be in the order of 4 to 1 in order to properly deform and seat the seal. It is difficult to find a material which can be surface-treated in a manner to provide this large a difference in coefficient of friction. Therefore, the prior art couplings generally utilize a seal which is made from two different materials. Even when such differences can be provided in a single material, it is difficult and expensive. In addition, special care in storage and handling is required to prevent loss of these properties due to age and weathering.
The present invention consists of the selection of a combination of materials and design constants in a pipe coupling so that a moderate difference in the coefficients of friction on the two surfaces of a seal used in the coupling will insure satisfactory self-locking operation. Therefore, the seal may be fabricated out of a single material, relying upon surface treatment of one of its sides to give the proper coefficient of friction.
Accordingly, it is the general purpose of the present invention to provide a pipe coupling for joining lengths of pipe which permits easy assembly of the pipe parts, but which prevents separation once they are assembled.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe which does not require special skills to install.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe which will join and seal the pipe lengths simultaneously.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe which is self-locking, preventing disassembly of the lengths of the pipe without destruction of the seal.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe wherein the seal can be fabricated from a common, low cost, rubber type material.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe wherein the coupling properties are not lessened due to weathering or extended underground placement.
It is a further purpose of the present invention to provide a pipe coupling for joining lengths of pipe not requiring special storage or handling procedures before use.